YouTube user DemonStrate made a speedrun through Portal in under ten minutes using glitches and exploits but nothing that's technically cheating. He used corner glitching to transport around the map, and he interrupted cutscenes and scripted events to save time. It looks like he spent the most time waiting in the elevator. Also, he found the cake. No, really, he did. It's in a part of the map found while corner glitching. You can see the cake in the first video after the jump. No lie.
Also after the jump is the newest trailer for Portal 2 which premiered at this year's Spike Video Game Awards. The cake awaits:
This is a triumph. I'm making a note here: HUGE SUCCESS.